The present invention relates to a pretensioner for vehicle seat belt systems, and in particular to a trigger for operating a pretensioner.
In the seat belt systems provided on a vehicle, such as an automobile, a pretensioner for tightening the belt is furnished in some cases for restraining the body of an occupant more firmly in an emergency. There are various types of pretensioners, such as those that rotate the belt reel of a seat belt retractor, those that directly pull the belt into a loop, or those that pull on the buckle. As the driving mechanism for such pretensioners, it is known to use a piston/cylinder operated by gunpowder or to use a spring. A driving mechanism using gunpowder requires an electric trigger to operate, and this involves an increased cost. For this reason, a spring-type pretensioner with a purely mechanical structure is preferred.
However, the driving mechanism to operate the pretensioner must have a sufficient stroke length and operating force to apply pretension to the belt. Particularly when a spring is used in the driving mechanism, a powerful spring must be used. The preload for such spring is high, and in order to release the preload, a trigger mechanism capable of exerting considerable operating force and an acceleration detecting sensor that outputs a mechanical signal large enough for operating the trigger mechanism are required.
In the past, the mechanical sensors have been disclosed by the Provisional Japanese Utility Model Publications No. 90159/1982 and No. 33060/1983; Japanese Utility Model Publication No. 35017/1988; and Provisional Japanese Patent Publications No. 206765/1983, No. 164650/1989, and No. 164651/1989. According to all of these documents, an inertia body directly supported by a trigger is moved by inertial force to operate the trigger.
However, the conventional arrangement requires a large inertia body for obtaining sufficient sensor output and a lever with a long arm for amplifying the sensor output to exert a high operating force. This results in a large size and a heavy weight of these mechanisms associated with the pretensioner.